Chess engine: Eubos 2.8

- February 19, 2022

Eubos - a basic Java chess engine, written for kicks. Uses jcpi for the UCI protocol parts. Kind of weak, doesn't evaluate for king safety, for example. Now uses transpostion hashing, but because it runs in the Java VM on a bog standard PC, doesn't search very deeply (around 100K Nodes/s, though this is actually quite hard to evaluate due to the hashing).

Author: Chris Bolt Rating CEDR=2069

v.2.8

This is mainly a bug fix release.

I found a subtle defect where the best move at a ply from the principal continuation could become corrupted. In practice, this meant that Eubos would sometimes search the naive best move from a static move order rather than the historical best move from the previous depth of the iterative deepening. If this happened to be a losing capture that caused an aspiration window fail, then this could cause a bad move to be returned from the search, if Eubos ran out of time.

I estimate that fixing this defect adds at least 30 Elo points to the engine's strength.

I have also implemented revisions to the move ordering and evaluation function. Most notably scoring passed pawns on game phase as well as rank, so they become more valuable when there is less material.

I also use progressive widening of aspiration windows in the search in version 2.8.

To install Eubos as an engine in Arena:
1. Select Engines > Install New Engine
2. In the file browser dialog that appears, change the drop down to *.bat
3. Navigate to the Eubos binary location, select the Eubos.bat
4. Select UCI protocol to communicate with Eubos
5. That's it!

Eubos 2.8 download